1. Field
This disclosure relates to a photocatalyst dispersion element, a method for producing a photocatalyst dispersion element, a photocatalyst body, and a method for producing a photocatalyst body.
2. Background
Photocatalytic materials such as titanium dioxide have recently been drawing attention. A “photocatalytic material” is a substance having semiconductor-like properties, which is brought into an excited state and generates electron-hole pairs upon irradiation with light having an energy higher than the band gap energy between its conduction band and valence band.
For titanium dioxide, photoexcitation occurs upon irradiation with light having a wavelength of 387 nm or less, and electron-hole pairs are generated therein. Then, the electron-hole pair generates active oxygen species such as hydroxyl radicals and superoxide ions at the surface of the photocatalytic material and its neighborhood, and the oxidizing power of these active oxygen species leads to decomposition activity and hydrophilization. These actions can be used to achieve a self-cleaning effect, deodorizing effect, antibacterial effect and the like. Hence, various parts and products provided with photocatalytic materials have been proposed.
Here, in the case of titanium dioxide, which is a typical photocatalytic material, the main excitation light is ultraviolet radiation, causing the problem of failing to achieve sufficient performance indoors, where there is little ultraviolet radiation. Thus, investigation has been made on so-called visible light-responsive photocatalytic materials, such as tungsten oxide and cadmium sulfide.
When such a photocatalytic material is used in various parts and products, the photocatalytic material needs to be provided on a substrate surface. In such cases, conveniently, a liquid containing the photocatalytic material can be produced in advance and adhered to the substrate surface.
To this end, liquids and creams containing photocatalytic materials have been proposed (see JP-A-11-001620 (1999) and JP-A-2002-212464). In producing such a liquid or cream containing a photocatalytic material, the hydrogen ion exponent is often adjusted for the convenience of production.
However, the adjustment of the hydrogen ion exponent has been limited to the production process, and no consideration has been given to the effect that the hydrogen ion exponent of the produced liquid or cream itself exerts on the catalytic activity of the photocatalyst formed by adhering the photocatalyst dispersion element to the surface of the substrate.
Furthermore, no consideration has been given also to the effect that the concentration of the additive contained in the produced liquid or cream exerts on the catalytic activity of the photocatalyst formed by adhering the photocatalyst dispersion element to the surface of the substrate.
Moreover, no consideration has been given also to the effect that the main ingredient of the additive exerts on the catalytic activity of the photocatalyst formed by adhering the photocatalyst dispersion element to the surface of the substrate.
Thus, there has been a danger of decreasing the catalytic activity of the photocatalyst formed by adhering the photocatalyst dispersion element to the surface of the substrate.